The Genkai plant in the Saga Prefecture is currently offline for regular inspections and nuclear experts have expressed concern over its aging No. 1 reactor, which began operating in 1975, The Asahi Shimbun reported Saturday.
NISA dismissed those concerns saying the pressure vessel would not likely crack, even if it operated for another 60 years. The agency conducted numerous tests, including one in which pieces of metal left inside the reactor are tested for their ductile-brittle transition temperature.
A test done in 1993 showed a metal sample was 56 degrees, but a sample tested in 2009 was 98 degrees, or 14 degrees higher than higher than it should be, the newspaper reported.
"I just don't understand yet why the transition temperature is so high," said Hiromitsu Ino, professor emeritus of metal materials science at the University of Tokyo. "I have doubts about the (pressure vessel's) safety. The No. 1 reactor should not be put back in operation."